1. Field of the Invention
The present invention relates to a silica glass crucible which is used for the pulling up of silicon single crystals, and produces fewer pinholes in the silicon single crystals, and a method for pulling up a silicon single crystal using the same.
2. Description of Related Art
Silicon single crystals which are used as materials for a semiconductor material such as a silicon wafer and the like, are mainly produced according to a CZ method. This production method is a method of heating and melting a polycrystalline silicon placed in a silica glass crucible to obtain a molten silicon liquid, growing a single crystal at a high temperature using a seed crystal immersed in this liquid surface, slowly pulling up the single crystal, and growing a rod-shaped single crystal therefrom.
Since the silicon single crystal is always immersed in the molten liquid at the center of the crucible during the pulling up, when air bubbles floating from the inner surface of the crucible adhere to the interface between the silicon single crystal and the molten silicon liquid, the bubbles are introduced as they are, into the silicon single crystal as pinholes. The pinholes are bubbles contained in the silicon single crystal. In the process of slicing the silicon single crystal, any wafer discovered to have pinholes is discarded, and thus pinholes provide one of the causes of decreases in product yield.
As a technology of preventing pinholes in silicon single crystals, there is known a method of melting the polycrystalline silicon raw material placed in a silica crucible at a certain range of furnace internal pressure, and performing the pulling up of a silicon single crystal at a furnace internal pressure higher than the previous pressure (Patent Document 1). Furthermore, there is also known a method of fusing the raw material within a certain range of internal furnace pressure, and then performing the pulling up of a single crystal after the fusion of raw material, at a furnace internal pressure which is lower than the internal furnace pressure at the time of fusion (Patent Document 2).
[Patent Document 1] JP-A No. 05-9097
[Patent Document 2] JP-A No. 2000-169287
The two conventional methods for preventing pinholes are both methods of preventing the air bubbles from being caught up in the silicon single crystal, by regulating the furnace internal pressure during the fusion of polycrystalline silicon and during the pulling up when performing the pulling up of a silicon single crystal. However, since the raw material polycrystalline silicon is fused in a silica glass crucible, and a silicon single crystal is pulled up from the fused silicon in the crucible, the influence of the silica glass crucible is large. However, no sufficient investigation has been made heretofore on the influence of the properties of the silica glass crucible exerted on the pinholes.
The present invention is intended to characterize the conditions for a silica glass crucible, and according to an aspect of the present invention, there is provided a silica glass crucible allowing the silicon single crystal to have fewer pinholes.